Ionic vacuum pump

ABSTRACT

A glow discharge pumping device is disclosed having an anode, a sputter cathode, and additional electrode means for controlling the glow discharge. In one embodiment the additional electrode means are two apertured planar electrides positioned between the anode and the cathode. In another embodiment the cathode comprises a rod inside the anode, and the additional electrode means is a grid surrounding the cathode rod in the anode.

0 United States Patent H 1 H 1 3,746,474 Lloyd July 17, 1973 IONICVACUUM PUMP 3,614,264 10/1970 Gunther 417/49 [76] Inventor: William A.Lloyd, 1422 Longfellow Way, San Jose, Calif. 95129 PrimaryExaminer-William L. Freeh [22] Filed Apr 2 1971 Attorney-Leon F. Herbert[21] App]. No.: 130,815

Related U.S. Application Data [57] ABSTRACT [63] g g of 330,960 1963! Aglow discharge pumping device is disclosed having a done an anode, asputter cathode, and additional electrode means for controlling the glowdischarge. In one em [2?] bodimem the additional electrode means are twoamp i 417/48 5] tured planar electrides positioned between the anode 1 oare and the cathode. In another embodiment the cathode 56 R d comprisesa rod inside the anode, and the additional I I eferences electrode meansis a grid surrounding the cathoderod UNITED STATES PATENTS in the anode3,535,055

10/1970 Brubaker et al. 417/48 5 Claims, 7 Drawing Figures \l Z4 HIMIONIC VACUUM PUMP This application is a continuation of my copendingapplication, Ser. No. 330,960 filed Dec. 16, 1963, now abandoned.

The present invention relates in general to glow discharge devices andmore particularly to a method for increasing the pumping of noble gasesby increasing the effective ion sputtering of the devices. Thisincreased pumping is obtained by more effective ion sputtering andimproves the operating efficiency of devices utilizing the glowdischarge principle such as, for example, certain vacuum pumps.

Heretofore, vacuum pumps have been built with an anode having aplurality of glow discharge passageways therein and a cathode structurehaving for their principle of operation the establishment of a pluralityof glow discharges within the interior of the anode and between thecathode plates and having a magnetic field threaded through the anode.Positive ions produced by the glow discharge are directed against thecathode plates in the pump. The impinging ions produce sputtering of areactive cathode material. The sputtered material is collected upon theinterior surfaces of the pump where it serves to entrap molecules in thegaseous state coming in contact therewith. In this manner, the gaspressure within a vessel enclosing the cathode and anode elements isreduced. Vacuum pumps of this typeare disclosed and claimed in the US.Pat. No. 2,993,638 issuedto Lewis D. Hall, et al., for Electrical VacuumPump Apparatus andMethod.

However, one serious limitation to the above device is found in pumpingof noble gases. Such gases, argon, etc., being inert, do not chemicallycombine readily (getter) with the sputtered material as do the othergases. When anatom of inert gas collides with a free electron, an ion ofnoble gas is formed in a known manner. This ion of noble gas is buriedin the inner surface of the pump, Now if other ions later bombard thatsame region of the surface, there is a great chance that the ions ofnoble gas will become re-emitted. When the amount of re-emitted noblegases becomes equal tothe amount of buried ions, the optimum pumpinglevel of the vacuum pump is reached.

The principal object of the present invention therefore, is to provide anovel improved sputter ion vacuum pump device wherein the pumping ofnoble gas is in creased.

The main feature of the present invention is the insertion of a thirdelectrode or grid in between the cathode and anode to increase theburial of the noble gases.

Another feature of the present invention is the method wherebyre-emission or re-sputtering of buried gases is reduced."

Still another feature of the present invention is the provision of anauxiliary electrode or defocusing grid between the anode and thecathodeto defocus the ions so that maximum life of the pump is achieved.

Other features and advantages of the present invention will becomeapparent upon perusal of the specification taken in connection with theaccompanying drawing, wherein:

FIG. 1 is a plan view partly in cross-section of a novel electricalvacuum pump apparatus of the present invention,

FIG. 2 is a cross-sectional view of the structure of FIG. 1 taken alongline 2-2 in the direction of the arrows, FIG. 3 is an enlarged sectionview of the present invention showing an anode cell, the grid andcathode and the ion column therebetween,

FIG. 4 is another embodiment of the present invention showing a secondelectrode or defocusing grid with the ion column,

FIG. 5 is a plan view partly cross-section of another embodiment of thepresent invention,

FIG. 6 is a cross-sectional view of the structure of FIG. 5 taken alongline 5-5 in the direction of the arrows, and

FIG. 7 is an enlarged cross-sectional view of a portion of FIG. 6showing a cathode rod, transparent grid and transparent anode cell.

Referring now to FIGS. 1, 2 and 3 there is shown the novel electricalvacuum pump of the present invention. A shallow, rectangular, flanged,cup-shaped member 1 as of, for example, stainless steel is closed off atits flanged open end by a rectangular closure plate 3 welded about itsperiphery to the flanged portion 3 of member 1 thereby forming asubstantially rectangular vacuum tight envelope.

A rectangular cellular anode 4, as of, for example, titanium is carrieduponthe end of a conductive rod 5 as of, for example, stainless steel,which extends outwardly of the rectangular vacuum envelope through anaperture in a short side wall of cup-shaped member 1. The conductive rod5 is insulated from and carried by the vacuum envelope through theintermediaries of annular insulator frames or cylindrical insulator 6 asof, for example, alumina ceramic. The free end of the conductive rod 5serves to provide a terminal for applying the positive anode voltagewith-respect to two substantially rectangular cathode plates 7.

The cathode plates 7 are made of a reactive material and aremechanically locked into position against the large flat side walls ofthe cup-shaped member 1 via the intermediary of cathode spacer plates 8.The cathode spacer plates 8 as of,- for example, stainless steel areprovided with semi-cylindrical ears 9 struck therefrom and assuringproper spacing between the cathode plates 7. The cathode plates 7 may beof any one of a number of reactive cathode materials such as, forexample, titanium, chromium, zirconium, gadolinium and iron.

Another side wall of the cup-shapedmember l is apertured to receive ahollow conduit 10 which may be of any convenient inside diametercommensurate with the desired pumping speed. The hollow conduit 10communicates with the structure (not shown) which it is desired toevacuate.

Interspaced between anode 4 and cathode plates 7 are positioned tworectangular-shaped grid members 12 as of, for example, titanium. Therectangular grids 12 are carried along the end of conductive rods 13 asof, for example, stainless steel which stand outwardly of therectangular cup-shaped member 1 through apertures in a short side wallthereof. The conductive rods 13 are insulated from and carried by theeup-shaped member 3 through the intermediary of cylindricalinsu lators ll as of, for example, alumina ceramic. The free end of rod 13 serves toprovide a tenninal for applying an intermediate, positive grid voltagewith respect to the grounded cathode plates 7 and positive anodes 4.

Grid plates 12 have a number of bored holes therein, the number of holes15 equalling the number of annular cells of anode 4 to permit gasdischarge flow between the cathodes 7 and the anode 4.

As an alternative, grid members 12 may consist of a mesh of titaniumwire (not shown), woven together to form rectangles made of titaniumwire the same size as the anode cells.

A permanent magnet 29 is positioned with respect to the rectangularvacuum envelope 3 such that the magnetic field of the magnet 29 threadsthrough the individual cellular elements of the anode 4 in substantialparallelism to the longitudinal axis thereof. The strength of themagnetic field is related to the diameter of the individual cellularanode compartments.

In operation of the present invention, the grid 12 between the anode 4and cathode 7 is of an intermediate positive potential. As a highpositive potential is applied to the anode 4 and an intermediatepotential is applied to the grid, free electrons trapped in the spacebetween grid 12 and the anode 4 will move to the more positive element,anode 4. However, the magnetic field caused by permanent magnets 29 willcause the electrons to spiral. It is during this spiraling that theelectrons collide with atoms of gas in the chamber in and around anode 4and between anode 4 and grid 12. This collision will produce more freeelectrons, and further result in positive ions being produced. The ions,being positive, are attracted to the less positive grid 12. Most ions I,as seen in FIG. 3, will pass through the apertures in the grid 12 andstrike the grounded cathode 7 with high energy, the ion energy beingequal to the difference in potential between anode 4 and cathode 7. Theions will strike cathode 7 with a great velocity and cause a largeamount of the reactive cathode material to be sputtered. Some of thesputtered material is then collected upon the interior structure of thepump as, for example, the cathode 7 or the grid 12 where they serve toentrap molecules in the gaseous state coming in contact therewith. Alarge amount of the sputtered material will pass back up through thegrid apertures in a cosine type distribution and collect upon theopposite grids. This sputtered material will serve to entrap gaseousmaterials thereon but will not be as likely to be reemitted as gasesburied on other pump surfaces.

If, for example, the anode 4 was at a 9,000 volt positive potential andthe grid 12 at 8,000 volt positive potential, free electrons in andaround anode 4 and the grid 12 will have 1,000 electron volts of energy.The positive ions which pass through the apertures in the grid 12,bombarding the cathode 7 will have 9,000 ion volts of energy. From thisit may be seen that electrons having a relatively low (1,000 electronvolts) energy will produce ions with a very high (9,000 ion volts)energy. It may be seen therefore that the ions which do not pass throughthe apertures in grid l2 will be relatively low energy (L000 ion volts)and will cause little sputtering from that grid electrode.

In the present invention, most of the sputtering will occur at thecathode while most of the burial of gas will take place on the grids andanode. In this way, smaller amounts of buried gas will be re-emittedthereby increasing the overall optimum pumping level of the pump.

In FIG. 4 of the present invention, an auxiliary grid 22' is showninserted between cathode 27 and grid 22. The purpose of auxiliary grid22' is to defocus the ions I, as seen in FIG. 4, so that the ions willbombard the cathode over a larger area so that the cathode areaavailable for sputtering and burial of gaseous material will be spreadover more of the cathode, thus achieving more effective sputtering andlonger cathode life. This defocusing may be effected by either applyinga positive potential with respect to cathode 27 to grid 22 causing theion columns to become over-focused or to apply a negative potential withrespect to cathode 27 and spread out the positive ions.

Referring now to FIGS. 5, 6 and 7, there is shown another embodiment ofthe present invention. A shallow, rectangular, flanged, cup-shapedmember 31 as of, for example, stainless steel, is closed off at itsflanged open end by a rectangular closure plate 33 welded about itsperiphery to the flanged portion 33' of member 31 thereby forming asubstantially rectangular vacuum tight envelope similar to the envelopereferred to in FIG. 1.

A transparent, rectangular, cellular anode 34 as of, for example,titanium, is carried upon the end of a conductive rod 35 as of, forexample, stainless steel, which extends outwardly of the rectangularvacuum envelope through an aperture in the short sidewall of cup-shapedmember 31. The conductive rod 35 is insulated from and carried by thevacuum envelope through the intermediaries of annular insulator frame orcylindrical insulator 36 as of, for example, alumina ceramic. The freeend of the conductive rod 35 serves to provide a terminal for applying apositive anode voltage with respect to cathode rods 37 and cathode plate37'.

Cathode plate 37' is made of a reactive material and is mechanicallylocked into position against the rectangular closure plate 33 via theintermediary of cathode spacer plates 38. The cathode spacer plates 38as of, for example, stainless steel, are provided with semicylindricalears 39 struck therefrom and insuring proper spacing of cathode plate37' from anode 34. As best seen in FIG. 7, cathode rods 37 extenddownward from cathode plate 37' into the rectangular cellular anode 34.Cathode rods 37 may be removeably fitted into cathode plate 37 by anydesired method for easy replacement if deemed desirable.

Another sidewall of the cup-shaped member 31 is apertured to receive ahollow conduit 40 which may be of any convenient inside diametercommensurate with the desired pumping speed. The hollow conduit 40communicates with the structure (not shown) which is desired toevacuate.

Interspaced between anode cells 34 and cathode rods 37 as best seen inFIG. 7, are positioned rectangular cellular grids 42 as of, for example,titanium, the rectangular cellular grids 42 are carried by means of astainless steel frame 42' which is carried along the ends of aconductive rod 43 as of, for example, stainless steel, which standsoutwardly of the rectangular cupshaped member 31 to apertures in a shortsidewall thereof. The conductive rod 43 is insulated from and carried bythe cup-shaped member 33 through the intermediary of a cylindricalinsulator 41 as of, for example, alumina ceramic and is fixedly securedto grid frame 42' by means of clamp 45. The free end of rod 43 serves toprovide a terminal for applying an intermediate positive grid voltagewith respect to the grounded cathode rods 37 and plate 37' and thepositive anodes 34. Grid plates 42 are made of strips of interwovenstrips of titanium to permit gas discharge glow between cathode rods 37and the anodes 34.

A permanent magnet 49 is positioned with respect to the rectangularvacuum envelope 33 such that the magnetic field of the magnet 49 threadsthrough the individual cellular elements of anode 4 substantiallyparallel to the longitudinal axis thereof. The strength of the magneticfield is related to the diameter of the individual cellular anodecompartments.

The operation of the embodiment of FIGS. 5, 6 and 7 is such that thegrid 42 is of an intermediary potential between the positive potentialof anode 34 and the grounded potential of cathode rods 37. The maindifference in the present embodiment is that a magnetron effect will bethe result of the present configuration, that is, electrons will becollected on the outer surface of the grid and of the anode instead of aPenning type discharge as seen in FIGS. l-4.

If, for example, the anode 34 was at a 9,000 volt positive potential andthe grid 42 at 8,000 volts positive potential free electrons in andaround the anode 34 and the grid 42 would have 1,000 electron volts ofenergy. The positive ions created between anode 34 and grid 42 will passthrough the apertures in the grid 42, and bombard the cathode rod 37with 9,000 ion volts of energy. These high energy ions will cause muchsputtering from the reactive material of cathode rods 37. Much of thesputtered material will pass back through the grids 42 due to the cosinedistribution of the sputtered material and pass through the griddedanodes 34 and be collected on the surfaces of grids of neighboring unitcells.

Now ions which do not pass through the apertures in grid 42 will strikethat grid with a relatively low energy (1,000 ion volts) and will beburied therein and cause very little sputtering from the outer surfacesof that grid electrode. Therefore, most of the sputtering will occur atthe cathode while most of the ion burial and covering over of sputteredmaterial will take place on the side of the grid away from the cathoderods. In this way very small amounts of gas will be re-emitted therebyincreasing the over-all optimum pumping level of the pump. a It may beseen from the foregoing disclosure that two improved vacuum pumps areshown having high energy ions which strike the sputtering cathode toincrease the sputtering and low energy ions of noble gases are buried atlow velocity on the grid and are covered over by sputtered material fromthe cathodes thereby increasing pumping of the pump. 7

Since many changes could be made in the above construction and manyapparently widely different embodiments of this invention could be madewithout departing from the scope thereof, it is intended that all mattercontained in the above description or shown in the accompanyingdrawingsshall be interpreted as illustrative and not in a limiting sense.

What is claimed is: a y

1. A sputter cathode type ionic vacuum pump apparatus including: avacuum-tight envelope adapted to be connected to a structure it isdesired to evacuate; an apertured anode electrode contained within saidenvelope; a pair of sputter cathode electrodes disposed on oppositesides of said anode electrode, coaxial therewith and contained withinsaid envelope; a first pair of apertured collector electrodes, disposedon opposite sides of said anode electrode, coaxial therewith, eachpositioned between said anode electrode and a respective one of saidsputter cathode electrodes andcontained within said envelope; means forsupplying operating potentials to said anode and sputter cathodeelectrodes so as to cause a glow discharge therebetween, said first pairof apertured electrodes being positioned within said glow discharge;means for supplying operating potential to said first pair of aperturedelectrodes intermediate with respect to said anode electrode and saidsputter cathode electrode potentials; means for producing and directinga magnetic field through said anode electrode; and a second pair ofapertured electrodes positioned within said envelope on opposite sidesof said anode electrode, each of said second pair of aperturedelectrodes being positioned between one of said first pair of aperturedelectrodes and the adjacent cathode electrode.

2. The apparatus according to claim 1 wherein, said anode electrode issubdivided into a plurality of lesser hollow open-ended compartmentsformed by holes ex tending through said anode electrode defining aplurality of glow discharge passageways therewithin, said first pair ofapertured electrodes includes a plurality of apertures aligned with theopen-ended compartments of said anode electrode for passage of said glowdischarge therethrough, the apertures in said first pair of aperturedelectrodes being smaller than the holes through said anode electrode topermit interception of a portion of the ions in said confined glowdischarge so as to cause sputtering from said first pair of aperturedelectrodes.

3. The apparatus according to claim 1 including means for applying apositive potential to said second pair of apertured electrodes relativeto said cathode electrodes.

4. The apparatus according to claim 1 including means for applying anegative potential to said second pair of apertured electrodes relativeto said cathode electrodes.

5. A sputter cathode type ionic vacuum pump apparatus including; avacuum-tight envelope adapted to be connected to a structure it isdesired to evacuate; an anode electrode contained within said envelopedivided into a plurality of hollow, open-ended, walled compartmentsformed by holes extending through said anode electrode, the walls ofsaid compartments being apertured; a sputter cathode electrode containedwithin said envelope and including a plurality of rod members extendinginto said open-ended compartments of said anode electrode in aspaced-apart manner; a collector electrode contained within saidenvelope including a plurality of cellular grids disposed within arespective one of said open-ended compartments of said anode electrodeabout a respective one of said rod members; means for supplyingoperating potentials to said anode and sputter cathode electrodes so asto cause a glow discharge therebetween; means for supplying operatingpotential to said collector electrode intermediate with respect to saidanode electrode and said sputter cathode electrode potentials; and meansfor producing and directing a magnetic field through said anodeelectrode.

II t t 4 4

1. A sputter cathode type ionic vacuum pump apparatus including: avacuum-tight envelope adapted to be connected to a structure it isdesired to evacuate; an apertured anode electrode contained within saidenvelope; a pair of sputter cathode electrodes disposed on oppositesides of said anode electrode, coaxial therewith and contained withinsaid envelope; a first pair of apertured collector electrodes, disposedon opposite sides of said anode electrode, coaxial therewith, eachpositioned between said anode electrode and a respective one of saidsputter cathode electrodes and contained within said envelope; means forsupplying operating potentials to said anode and sputter cathodeelectrodes so as to cause a glow discharge therebetween, said first pairof apertured electrodes being positioned within said glow discharge;means for supplying operating potential to said first pair of aperturedelectrodes intermediate with respect to said anode electrode and saidsputter cathode electrode potentials; means for producing and directinga magnetic field through said anode electrode; and a second pair ofapertured electrodes positioned within said envelope on opposite sidesof said anode electrode, each of said second pair of aperturedelectrodes being positioned between one of said first pair of aperturedelectrodes and the adjacent cathode electrode.
 2. The apparatusaccording to claim 1 wherein, said anode electrode is subdivided into aplurality of lesser hollow open-ended compartments formed by holesextending through said anode electrode defining a plurality of glowdischarge passageways therewithin, said first pair of aperturedelectrodes includes a plurality of apertures aligned with the open-endedcompartments of said anode electrode for passage of said glow dischargetherethrough, the apertures in said first pair of apertured electrodesbeing smaller than the holes through said anode electrode to permitinterception of a portion of the ions in said confined glow discharge soas to cause sputtering from said first pair of apertured electrodes. 3.The apparatus according to claim 1 including means for applying apositive potential to said second pair of apertured electrodes relativeto said cathode electrodes.
 4. The apparatus according to claim 1including means for applying a negative potential to said second pair ofapertured electrodes relative to said cathode electrodes.
 5. A sputtercathode type ionic vacuum pump apparatus including; a vacuum-tightenvelope adapted to be connected to a structure it is desired toevacuate; an anode electrode contained within said envelope divided intoa plurality of hollow, opeN-ended, walled compartments formed by holesextending through said anode electrode, the walls of said compartmentsbeing apertured; a sputter cathode electrode contained within saidenvelope and including a plurality of rod members extending into saidopen-ended compartments of said anode electrode in a spaced-apartmanner; a collector electrode contained within said envelope including aplurality of cellular grids disposed within a respective one of saidopen-ended compartments of said anode electrode about a respective oneof said rod members; means for supplying operating potentials to saidanode and sputter cathode electrodes so as to cause a glow dischargetherebetween; means for supplying operating potential to said collectorelectrode intermediate with respect to said anode electrode and saidsputter cathode electrode potentials; and means for producing anddirecting a magnetic field through said anode electrode.